1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to an apparatus and method for transmitting a power headroom report in a communication system supporting multi-carriers.
2. Discussion of the Related Art
First of all, in the following description, 3GPP LTE (3rd generation partnership projecting long term evolution, hereinafter abbreviated LTE) is schematically explained as an example of a mobile communication system to which the present invention is applicable.
FIG. 1 is a schematic diagram of E-UMTS network structure as an example of a mobile communication system. In particular, E-UMTS (evolved universal mobile telecommunications system) is the system evolved from a conventional UMTS (universal mobile telecommunications system) and its basic standardization is ongoing by 3GPP. Generally, E-UMTS can be called LTE (long term evolution) system.
Referring to FIG. 1, E-UMTS consists of a user equipment (UE), base stations (eNode B: eNB) 110a and 110b and an access gateway (AG) provided to an end terminal of a network (E-UTRAN) to be connected to an external network. The base station is able to simultaneously transmit multi-data streams for a broadcast service, a multicast service and/or a unicast service.
At least one or more cells exist in one base station. The cell is set to one of bandwidths including 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz and the like and then provides an uplink or downlink transmission service to a plurality of user equipments. Different cells can be set to provide different bandwidths, respectively. A base station controls data transmissions and receptions for a plurality of user equipments. A base station sends downlink scheduling information on downlink (DL) data to inform a corresponding user equipment of time/frequency region for transmitting data to the corresponding user equipment, coding, data size, HARQ (hybrid automatic repeat and request) relevant information and the like. And, the base station sends uplink scheduling information on uplink (UL) data to a corresponding user equipment to inform the corresponding user equipment of time/frequency region available for the corresponding user equipment, coding, data size, HARQ relevant information and the like. An interface for user or control traffic transmission is usable between base stations. A core network (CN) can consist of an AG, a network node for user registration of a user equipment and the like. The AG manages mobility of the user equipment by a unit of TA (tracking area) including a plurality of cells.
The wireless communication technology has been developed up to LTE based on WCDMA (wideband code division multiple access) but the demands and expectations of users and service providers are continuously rising. Since other radio access technologies keep being developed, new technological evolution is requested to become competitive in the future. For this, reduction of cost per bit, service availability increase, flexible frequency band use, simple-structure and open interface, reasonable power consumption of user equipment and the like are required.
Recently, 3GPP is working on the standardization of the next technology for LTE. In the present specification of the present invention, the next technology shall be named ‘LIE-Advanced’ or ‘LTE-A’. Major differences between the LTE system and the LTE-A system include a system bandwidth difference and a relay introduction.
The LTE-A system has a goal to support a broadband of maximum 100 MHz. For this, the LTE-A system uses carrier aggregation or bandwidth aggregation to achieving a broadband using a plurality of frequency blocks. The carrier aggregation enables a plurality of frequency blocks to be used as one large logic frequency band to use a wider frequency band. A bandwidth of each frequency block can be defined based on a system block used by the LTE system. And, each frequency block is transmitted using a component carrier.
However, as the LET-S system of the next communication system adopts the carrier aggregation, the demand for a method of transmitting a power headroom report of a user equipment in a mobile communication system supporting multi-carriers is rising.